In 1967-68, Sanderson joined the Boston Bruins full-time in the NHL. He played in 71 games, contributing 24 goals and 49 points. Sanderson also collected 98 PIM in his rookie season, establishing himself as a "tough guy" in the league.[1] At season's end, Sanderson was awarded the Calder Memorial Trophy as the NHL's Rookie of the Year, an honor that Orr won the previous year, giving the Bruins their second consecutive Calder Memorial Trophy.[5]

Although he had been a leading scorer in junior hockey, his role on the high-scoring Bruins was to centre their defensive line with wingers Ed Westfall and Don Marcotte. The line excelled at killing penalties.[6] In 1969-70, the Boston Bruins made it to the Stanley Cup Finals, where they faced off against the St. Louis Blues. The series went to a fourth game where Boston was leading the best-of-seven series three games to none. After three periods, the teams were tied 3-3, and the fourth game would need overtime. After only 40 seconds of overtime, Bobby Orr scored the game-winning goal[7] clinching the Bruins' first Stanley Cup in 29 years.[8] Bobby Orr's goal went on to become one of the most famous goals in hockey history.[7] Often overlooked though was that Sanderson was the player who passed the puck to Bobby Orr for that goal.[9]

During his time in Boston, Sanderson became a celebrity. Sanderson received much publicity for his flamboyant "mod" lifestyle as seen by his owning a Rolls-Royce car.[10] Named by Cosmopolitan Magazine as one of the sexiest men in America, he was the subject of gossip columns, a frequent guest on television talk shows, and regularly photographed in the company of numerous beautiful women.[11] Sanderson was in the public eye enough that it has been reported New York Yankees' shortstop Derek Jeter was named after him. This has, however, been denied by Jeter himself in an interview on MLB.com.[12] Derek Jeter's father's first name is Sanderson; as a result, this is more likely to be source of his middle name. Sanderson would help the Bruins finish first in the league the next two seasons (1970-71 and 1971-72). He also helped the Bruins win the Stanley Cup in 1971-72 against the New York Rangers.[13]

In the summer of 1972, Sanderson made headlines around the world of sports when he signed what was then the richest contract in professional sports history. The Philadelphia Blazers of the rival league World Hockey Association signed Sanderson to a $2.6 million contract, making him the highest-paid athlete in the world at the time.[14] His time with the Blazers was disastrous, as, plagued with injuries, Sanderson appeared in only eight games, recording six points. The Blazers management team had had enough and at the end of the season, Sanderson was paid $1 million to return to the Bruins.[15]

After being kicked off the Blazers' roster, Sanderson played with the Bruins for two seasons, in which he suited up for only 54 games out of a possible 156. The Bruins, seeing no future for Sanderson, sent him down to the American Hockey League with the Boston Braves for three games before trading him to the New York Rangers in 1974-75. It was with the Rangers that his alcoholism started.[16] Meanwhile, in a distraction from his hockey career, along with New England Patriots receiver Jim Colclough, and the New York Jets star football quarterback Joe Namath, Sanderson opened "Bachelors III", a trendy nightclub on New York City’s Upper East Side. Negative publicity over some of the club's less than reputable patrons led to problems and eventually Sanderson had to get out of what went from a "goldmine" to a money-losing venture.[17] This would start a downward spiral in which Sanderson would bounce from team to team, never being able to stay with a team for more than two full seasons because mainly of his addiction to alcohol. Although Sanderson had a good first season with the Rangers by recording 50 points in 75 games, he would be traded eight games in, to the St. Louis Blues next season. In St. Louis, Sanderson set career highs in assists and points scored in a season with 43 assists and 67 points. Again Sanderson's problems with alcohol and his recurring knee problems would lead Blues management to trade him in 1976-77 to the Vancouver Canucks. Struggling with his addiction to alcohol, Sanderson managed to score 16 points in 16 games with the Canucks, but he was still sent to the minors. As was the case with the Blues, the Canucks' impatience with Sanderson's struggle with alcohol and his knee problems led them to the decision not to re-sign him. The Pittsburgh Penguins would sign Sanderson as a free agent in 1977-78. Sanderson would play 13 games with the Penguins and eight games in the minors before retiring.[18]

During his career, Sanderson made many bad investments, losing millions of dollars which led him to be quite broke upon his retirement. Along with his substance abuse problems, Sanderson wound up penniless, one time sleeping on a New York City park bench. He was also in poor health, and crippled to the point he had to get around on crutches.[15] Forced to accept the charity of friends who gave him a place to live, several years after his retirement, publicity about his situation brought a second chance from the goodwill of people in the city of Boston, a place of which Bobby Orr said the fans and citizens were the most loyal and decent in the world. Orr spent his own money to check Sanderson and several Bruins personnel into rehab.[19] Sanderson entered rehab in 1979 and beat his addictions and took a job as a professional sports broadcaster. He worked for ten years in broadcasting with NESN. Wanting to make sure that other hockey players would not follow his dark path, Sanderson, organized The Professionals Group at State Street Global Advisors, where he was Director of The Sports Group that provided professional financial advice to athletes in the 90s.[19]

Sanderson is currently Managing Director of The Sports Group in Boston. His team works with athletes and high-net-worth individuals.[20] He is involved with a variety of charitable organizations and makes a number of guest appearances at charitable events to help raise awareness and funding for their cause. His autobiography, 'Crossing the Line: The Outrageous Story of a Hockey Original,' written with Kevin Shea, was released in October 2012 by Triumph in the United States and by HarperCollins Canada.[21]